Figure 2.

Kinetics of the effect of quercetin on glucose-induced insulin secretion and extracellular signal-regulated kinase (ERK)1/2 phosphorylation in INS-1 cells. INS-1 cells were incubated in the presence of 8.3 mmol·L⁻¹ glucose and in the absence or presence of 20 µmol·L⁻¹ quercetin for various periods, quercetin being added 5, 10, 20, 40 or 60 min before the end of incubation. Insulin secretion was quantified by the homogeneous time resolved fluorescence method. Western blotting experiments were performed; intensity of each band was quantified using a densitometric imager and relative band intensity was calculated as the ratio (phospho ERK1/2/ERK1/2). Data are expressed relative to the response obtained in the absence of quercetin (time = 0), taken as 100%. Results are presented as mean ± SEM (n = 4). A multiple comparison analysis of data was performed for each kind of experiment (insulin secretion or ERK1/2 phosphorylation). Bars with the same letter do not differ significantly (P > 0.05).